Combined in vivo amperometric oximetry and electrophysiology in a single sensor: A tool for epilepsy research

Seizures are paroxysmal events in which increased neuronal activity is accompanied by an increase in localized energetic demand. The ability to simultaneously record electrical and chemical events using a single sensor poses a promising approach to identify seizure onset zones in the brain. In the present work, we used ceramic-based platinum microelectrode arrays (MEAs) to perform high-frequency amperometric recording of local pO₂ and local field potential (LFP)-related currents during seizures in the hippocampus of chronically implanted freely moving rats. Resting levels of O₂ in the rodent brain varied between 6.6 ± 0.7 μM in the dentate gyrus (DG) region of the hippocampus and 22.1 ± 4.9 μM in the cerebral cortex. We also observed an expected increase in hippocampal pO₂ (15 ± 4% from baseline) in response to tail pinch stress paradigm. Finally, induction of status epilepticus by intrahippocampal injection of pilocarpine induced biphasic changes in pO₂ in the hippocampus. The initial dip at seizure onset (ΔO₂ = -4.5 ± 0.7 μM) was followed by a prolonged hyperoxygenation phase (ΔO₂ = +10.4 ± 2.9 μM). By acquiring the amperometry signal with a high sampling rate of 100 Hz we decomposed the raw signal in an oximetry recording (<1 Hz) and LFP recording (>1 Hz), demonstrating that each individual Pt site can simultaneously report changes in local pO₂ and LFP-related currents during pilocarpine-induced seizure activity. This has high potential for translation into the clinical setting supported on intracranial grid or strip electrodes.